1. Field of the Invention
The present invention relates to a resource reservation system and method in a wireless network. More particularly, the present invention relates to a resource reservation system and method in a wireless network, which provides resource management under consideration of the mobility of a mobile node.
2. Description of the Related Art
A resource reservation state management scheme is employed in a wireless network in order to ensure Quality of Service (hereinafter referred to as “QoS”). This resource reservation state management scheme is a state management scheme in which resources are reserved in advance and used session by session.
Such a state management scheme may be largely classified into a hard-state-based scheme and a soft-state-based scheme. In the hard-state-based state management scheme, resources according to a corresponding session are released by a session release request issued from the subject of the corresponding session. In the soft-state-based state management scheme, resources according to a corresponding session are released by a session maintenance request cyclically issued from the subject of the corresponding session.
FIG. 1 is a view comparing the performance of the hard-state-based state management scheme with that of the soft-state-based state management scheme.
As seen from FIG. 1, the hard-state-based state management scheme shows relatively better performance when a network condition is good, but the soft-state-based state management scheme shows relatively better performance when a network condition is not good.
A typical example of the soft-state-based state management scheme is a Resource Reservation Protocol (hereinafter referred to as “RSVP”). The RSVP defines procedures for ensuring resources in order to guarantee requirements of Internet application services. The RSVP operates on a packet belonging to a specific session, and one session is defined by a destination IP (Internet Protocol) address, a transport protocol type and a destination port number. The RSVP can be said to be a signal protocol on the Internet for setting up routing states in routers in order to satisfy requirements of services defined in an Internet integrated service model.
The RSVP operates in a simplex mode. That is, both end hosts request resources in different directions. Thus, in the RSVP, a resource request is dominated by a recipient.
For example, assuming that the subject of reservation is a Mobile Node (hereinafter referred to as “MN”), the MN cyclically transmits a refresh message. The refresh message is a message requesting the maintenance of a current session. A cycle, in which the refresh message is transmitted, is a refresh interval, and the refresh interval is determined when a corresponding session is created. The refresh interval is fixedly given to a corresponding session on a session-by-session basis.
The refresh message is transferred to a Correspondent Node (hereinafter referred to as “CN”) through a path of routers which is established for a current session. Among the routers, a router, to which the MN is initially connected, is denominated as a serving router, and routers existing between the serving router and the CN are denominated as relay routers. The serving and relay routers perform resource allocation according to periods on the path established for the corresponding session.
If a refresh message is not received until a set refresh interval elapses, the serving and relay routers and the CN withdraw resources allocated for a corresponding session. The withdrawal of the resources allocated for the corresponding session means the termination of the corresponding session. A state time-out interval when the corresponding session terminates is determined based on a refresh interval. In general, the state time-out interval is determined as an integer times of the refresh interval.
In a wireless network, the mobility of a MN must be considered. Thus, a state management scheme in a wireless network is also required to consider the mobility of a MN.
FIG. 2 explains an RSVP operation under consideration of a situation where an MN is handed off in the existing wireless network.
Referring to FIG. 2, the MN transmits a refresh message at transmission points t0, t1, . . . , tn, tn+1 specified by a refresh interval Trefresh. The refresh message propagates through a path corresponding to a corresponding session. If handoff occurs between tn and tn+1, the MN establishes a new path through a target router to which the MN is to move. In order to establish the new path corresponding to the occurrence of the handoff, a certain time, called a delay time Tho, is required.
However, although the handoff is completed, the old path still exists. Resources occupied by the old path are released when a state time-out interval elapses from tn.
Therefore, the old path and the new path co-exist from a point of time when the handoff is completed to a point of time when the state time-out interval elapses. A period where both the paths co-exist is denominated a resource waste period Twaste. That is, the resources occupied by the old path after the new path is established can be considered a loss until they are released.
In order to prevent such a resource loss, it must be possible to rapidly release resources occupied by an old path when a new path is established by handoff.
To this end, among relay routers, a relay router where a new path branches off from an old path (hereinafter referred to as “crossover router”) can request to forcedly release resources occupied by the old path which is connected so far as a serving router. With regard to this, since the crossover router is not the subject of session setup for a corresponding session, an authorization problem may be caused when the resources occupied by the old path are forcedly released. Thus, in order that the crossover router can request to forcedly release the resources occupied by the old path, a separate authorization process is required.
In another way to rapidly release resources occupied by an old path, a refresh interval may be reduced. However, if a refresh interval is reduced, an MN must transmit relatively many refresh messages, which increases the amount of resources necessary for transmitting the refresh messages.
Accordingly, there is a need for an improved resource reservation system and method in a wireless network which provides resource management under consideration of the mobility of a mobile node.